Method for dehydrating a porous material

ABSTRACT

A method for dehydrating a porous material using electro-osmosis, includes applying a pattern of D.C. voltage pulses to an anode system embedded in the porous material, wherein the anode system is electrically interactive with a cathode structure embedded in earth, and wherein the pattern of D.C. voltage pulses, has a pulse period T in a range from about 3 to about 60 seconds, and each pulse period T includes a positive pulse duration of T+ from about 0.7 T to about 0.97 T, a negative pulse duration of T- from about 0.01 T to about 0.05 T, and a neutral pulse duration of T p  from about 0.02 T to about 0.25 T. In another embodiment, each pulse period includes two or more positive pulses separated by at least one of either a negative pulse or a neutral pulse, with the positive pulse duration being the combined duration of the two positive pulses.

BACKGROUND OF THE INVENTION

The present invention generally relates to a method for dehydratingporous materials, such as moist walls and/or floors of a masonry orconcrete structure, as well as the clay containment structure of alandfill, through the use of electro-osmosis. More particularly, thepresent invention relates to applying a D.C. voltage of a specific pulsepattern to an anode embedded in a porous material, and allowing thevoltage to travel through the porous material to a cathode embedded inearth.

Moisture problems in containment structures are common, particularly inbuilding structures located at least partially underground. In addition,modern day efforts to minimize building erection time often do not allowadequate drying time for concrete, leading to moisture problems in thebuilding structure. number of these methods require significant energyand time to achieve the marginal results.

The principle of electro-osmosis was discovered by Professor F. F. Reussin Moscow in 1807. Electro-osmosis employs a voltage potentialdifference between two points on opposite sides of a porous material. Ifthe porous structure of the material has been saturated by water, theporous materials assume a negative potential. This causes positive ionsin the water to locate around the porous materials to form a so-calledelectrical double layer. The positive ions will move towards a regionhaving a lower voltage potential. The positive ions are hydrated, andtherefore each ion carries a small amount of water, resulting in a waterflow toward the lower potential.

There have been a number of commercial attempts to dehydrate buildingstructures using electro-osmosis. In some European countries, aso-called "passive" electro-osmosis system has been employed, wherein anatural potential difference which is created between a moist materialand its surroundings is used. This type of installation has yieldedmarginal results.

In other types of electro-osmosis systems, a direct current orconventional alternating current has been used to generate a potentialdifference. With these systems, it is only possible to carry waterbetween the anode and cathode over a short period of time, because theforces after some period will reverse such that the electrolyte (water)is transported back to its origin. Efforts were thus directed towarddeveloping a system capable of functioning over an extended period oftime, without the so-called "zeta potential" being reversed, meaningthat the water returns back to the capillary material. A number ofsystem have been developed utilizing a pulsating direct current, that iswhere the current is switched between positive and negative potentials.Such systems are described in U.S. Pat. Nos. 5,368,709; 4,600,486; and5,015,351; as well as in Swedish patent applications 8106785-2 and8601888-4 (P. Eliassen), Swedish Pat. No. 450264 and Polish Pat. No.140265 (Basinsky et al.). These known systems have problems relating tothe durability of the electrodes on the anode side of the system becausethe anodes are easily corroded due to a reduction-oxidation phenomenon.In addition, these known systems have not balanced the energy of thepositive and negative pulses in voltage-seconds, also denoted asmagnetic flux, so that a maximum water flow out of porous material ofthe structure is obtained without having a further moisturizing of theporous material at a later time.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a novel method and apparatusfor dehydrating porous materials which sustains the transport of liquidin the desired direction.

It is a further object of the invention to provide an improvedelectro-osmotic method and apparatus for dehydrating porous materialswhich reduces the drying time and lowers the relative humidity comparedto known methods.

It is yet another object of the present invention to provide a novelelectro-osmotic method and apparatus for dehydrating porous materials toa lower relative humidity level than prior art methods and apparatus.

The above and other objects are accomplished according to the inventionby the provision of a method and apparatus for dehydrating a porousmaterial using electro-osmosis, including the steps of: applying apattern of D.C. voltage pulses to an anode system embedded in thematerial, the anode system being electrically interactive with a cathodestructure embedded in earth, wherein the pattern of D.C. voltage pulseshas a pulse period T in a range from about 3 to about 60 seconds, andeach pulse period includes a positive pulse duration T+ from about 0.7 Tto about 0.97 T, a negative pulse duration T- from about 0.01 T to about0.05 T and a neutral pulse duration T_(p) from about 0.02 T to about0.25 T.

It has been found that by utilizing a pulse pattern according to onepreferred embodiment of the invention, an osmotic pressure differentialfrom one side to the other of a structure made of porous material can besustained which is at least ten times greater than that possible withknown electro-osmotic techniques.

In accordance with another preferred embodiment of the invention, eachpulse period includes two or more positive pulses separated by at leastone of either a negative pulse or a neutral pulse, with the positivepulse duration T+ being the combined duration of the two positivepulses, an even greater osmotic pressure differential is developed.

Other objects, features and advantages of the invention will becomeapparent from the following detailed description of the invention whentaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a conventional environmental situationrelating to a building structure of masonry or concrete.

FIG. 2 is a diagram illustrating a basic layout of apparatus fordehydrating porous materials of a building structure which can beutilized for practicing the method of the invention.

FIG. 3 is a basic circuit diagram for practicing a method according tothe invention.

FIG. 4 is a block circuit diagram and circuit schematic for anelectrical circuit which can be utilized for carrying out a methodaccording to the invention.

FIG. 5A, which is labeled "Prior Art", is a signal diagram illustratinga prior art pulse pattern.

FIG. 5B illustrates a test setup that was used for conducting tests formeasuring osmotic pressure produced by different pulse patterns.

FIG. 6A is a signal diagram illustrating a pulse pattern according toone aspect of the present invention.

FIG. 6B is a signal pattern illustrating a pulse pattern according toanother aspect of the present invention.

FIG. 6C is a signal pattern illustrating a pulse pattern according toanother aspect of the present invention.

FIG. 7 is a graph showing water column rise in millimeters whichrepresents rising osmotic pressure over a period of days utilizingdifferent pulse patterns.

FIG. 8 illustrates a partial block diagram according to another aspectof the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, there is shown a structure 1 with walls 1a and afloor 1b comprising a porous material, such as masonry and/or concrete,located in the earth 2 below ground level. A conventional drain pipe 3is shown running from a roof (not shown) close to outer wall la. Waterwill therefore likely seep into the porous wall 1a. Some capillaryabsorption represented by the arrows in FIG. 1 of the water by the outerwall 1a and by the rest of the masonry structure can create highrelative humidity in the space enclosed by walls 1a. Insufficientventilation of the enclosed space will create a musty, damp atmosphererendering the space unsuitable for many uses.

FIG. 2, shows a similar building structure 1 which is wired for carryingout electro-osmotic dehydration. Specifically, a number of anodes 4 areprovided in the porous walls and/or in the floor of the undergroundbuilding structure. Preferably, the anodes are comprised of an inertmaterial such as a mixed metal oxide (MMO) ceramic wire anode. Such wireanodes can be obtained from Ceranode Technologies International, whichis a division of APS-Material, Inc., Dayton, Ohio, which sells such wireanodes under the trademark CerAnode. Alternatively, the anodes cancomprise conventional rubber graphite anodes which conduct current,according to Faraday's law, by movement of electronically conductivecarbon ions. One advantage of using a mixed metal oxide anode is that ithas a low dissolution rate on the order of one to 10 mg/amp-year. Incontrast, conventional rubber graphite anodes have a dissolution rate onthe order of 2 kg of carbon/amp-year and therefore have a relativelyshort life. The MMO wire anodes are preferably installed in thin, 1/16thinch wide grooves cut in the masonry in parallel lines several feetapart as generally shown by the dashed parallel lines in FIG. 2.

A common cathode 5 preferably comprises a copper clad steel rod embeddedin the ground as shown in FIG. 2. The anodes and cathode are connectedto a power control unit 6 which supplies a D.C. voltage pulse patternbetween the anodes 4 embedded in porous material of the buildingstructure and the cathode 5. By applying an appropriate D.C. voltagepulse pattern as discussed below, water travels from a positivepotential (+) at the wall to a negative potential (-) at the cathode.Water therefore flows out of the porous material and into the earth 2 asshown by the arrows in FIG. 2.

A simplified schematic of the electro-osmotic system is shown in FIG. 3,wherein like reference numerals are used to denote like components. InFIG. 3, the anodes 4' are in the form of rubberized graphite plugs asopposed to the wire anodes illustrated in FIG. 2.

FIG. 4 illustrates the power control unit 6 in more detail. As shown inFIG. 4, the power control unit 6 preferably includes a control unit 6A,a power unit 6B and an output unit 6C. The power unit 6B receives A.C.power at input terminals 12. The A.C. supply voltage is down-convertedin a transformer 13, rectified in a rectifier 14, and is suitablystabilized (e, by a conventional capacitor ) to deliver D.C. voltage,for example, 30 volts D.C. to an input 8A of an electronic switcharrangement 8 in the output unit 6C.

The control unit 6A preferably includes a programmable microprocessor 9,a program setting panel 10 and a control display 11. The microprocessor9 is suitably programmed for producing control signals on control lines16 which control the operation of electronic switches 17, 18, 19 and 20in switch arrangement 8 in output unit 6C. The program setting panel 10permits adjustments to be made in the parameters of the microprocessorprogram to adjust the control signals on control line 16 for producing adesired pulse pattern at the output of control unit 6C as will bediscussed below.

The direct voltage signal at input 8A is preferably coupled to a seriesconnection of electronic switches 17 and 19 and another seriesconnection of switches 18 and 20. Switches 17, 18, 19 and 20 are eachindividually controlled by a respective control line 16A, 16B, 16C and16D. Another control line 16E is optionally connected to a common node 7which is also connected to a terminal of each of switches 19 and 20. Aresistor 23 is connected between common node 7 and a ground electrode25.

FIG. 4 additionally shows two different sets +A and +B of anodes 4coupled by a line 27 to a node 29 between switches 17 and 19. Line 27 isconnected to a terminal of respective controllable relays 21 and 22which are selectively activated via control lines 16F and 16G forenergizing a selected one of the anode sets +A and +B. The commoncathode 5 in FIG. 4 is denoted by -A, -B which is connected by a line 31to a common node 33 between electronic switches 18 and 20. Multiple sets+A and +B of anodes are provided to utilize the overall working capacityof power control unit 6 and its associated circuitry. Different sets ofanodes will provide greater operational safety by reducing localizedcurrent and also increase dehydration capacity, however, the dehydrationprocess can take longer. Dehydration time can be reduced by increasingthe working capacity of the power control unit.

Selectively opening and closing switches 17, 18, 19 and 20 causes apositive, negative or neutral (zero voltage level) pulse to be conductedvia line 27 to one or both of the electrodes sets A and B, depending onwhether relays 21 and 22 are open or closed. For example, if switches 17and 20 are closed and switches 18 and 19 are open, the voltage input +25volts D.C. at input 8A will be applied across anodes +A and/or +Brelative to the cathode -A, -B. On the other hand, if switches 17 and 20are open and switches 18 and 19 are closed, the anode to cathodepotential is -25 volts D.C. A neutral or zero voltage level pulse can beproduced at the anodes by opening switches 17 and 18 and closing theswitches 19 and 20. It will be appreciated by those skilled in the artthat control lines 16A to 16D can be controlled by the microprocessor 9and program setting panel 10 to conduct control signals to switches 17to 20, thereby creating any desired pulse pattern of positive, negativeand neutral pulses at the anodes.

FIG. 5A illustrates a known pulse pattern which has been utilized in thepast for electro-osmotic dehydration. This conventional patterntypically includes a positive pulse duration T+ that is approximately0.7 T, a negative pulse duration T-of approximately 0.1 T, and a neutralpulse duration T_(p) of approximately 0.2 T. A pulse pattern of thistype is disclosed, for example, in U.S. Pat. No. 5,368,709. The pulsepattern duration disclosed in this patent is 1.4 seconds.

Using this conventional pulse pattern shown in FIG. 5A, with a pulseperiod of T equal to 3 seconds, it has been found that osmotic pressuregradually increases and levels out at relatively modest levels after afew days.

Referring to FIG. 5B, a laboratory experiment was conducted to measureosmotic pressure produced by different pulse patterns. The laboratorysetup included two tanks 30 and 32 of different sizes. The smaller tank32, which was bottomless, was supported within the larger tank 30 withthe upper edge 32a of the smaller or inner tank 32 spaced apart from theupper edge 30a of the outer tank 30, defining a gap 34. The interior ofthe inner tank 32 was communicated with the interior of the outer tankby a porous material 35, for this testing, a brick, which was installedin sealed relationship with the open bottom of the inner tank 32. Thetanks 30 and 32 were filled with water 36 to the same initial level 36aabove the brick 35. An anode 37 was placed in the outer tank 30. Acathode 38 was placed in the water 36 in the inner tank 32. The anode 37and the cathode 38 were connected to outputs of a control unit 39. Thecontrol unit created direct voltage pulse patterns at the anode 37relative to the cathode 38.

A pulse pattern having the characteristics of FIG. 5 with the positive,negative and neutral duration periods T+, T-, and T_(p), respectively,as discussed above, resulted in a 30 mm rise of the water level in thetank 32 containing the cathode 38. No further water level change wasobserved after about 48 hours. These test results are represented bycurve I in FIG. 7.

Surprising and convincing results based on extensive testing andverification of the effectiveness of preferred embodiments of thepresent invention have established that varying certain pulse parametersincreases dehydrating effectiveness.

A series of tests were conducted using a different set of pulseparameters for each test of the series of tests. For the testing, equalpositive and negative pulse magnitudes of 20, 40 and 66 volts were usedin the testing of each of several pulse patterns. In addition, for eachpulse pattern and each voltage magnitude, a test was

conducted for pulse pattern durations of 3, 6, 10, 20, 30 and 60seconds. In the following description, each pulse pattern is representedby a sequence of three numbers separated by a hyphen, wherein the firstnumber is the positive pulse duration T+, the second number is thenegative pulse duration T-, and the third number is the neutral pulseduration T_(p). For the initial testing, the pulse patterns that wereused in the testing were as follows:

    ______________________________________                                        60-15-25       80-10-10     70-10-20                                          75-10-15       85-5-5       90-5-5                                            ______________________________________                                    

In accordance with the convention referred to above, the pulse pattern60-15-25, for example, has a positive pulse duration T+ of 60, anegative pulse duration T- of 15, and a neutral pulse duration T_(p) of25. The testing was conducted for each of these six pulse patterns usingthe voltage magnitudes and pulse pattern durations stated above. Theduration of the test for each set of parameters was 48 hours.

The test results showed that changing the voltage magnitude did notsignificantly impact the amount of increase in the height of the waterin the inner tank. Moreover, the testing demonstrated that the bestresults were obtained when the duration of the pulse pattern was between6 and 10 seconds. In addition, more favorable results were obtained forpulse patterns in which the positive side pulses represented 90% or moreof the duration T of the pulse pattern.

Accordingly, further testing was conducted using pulse patterns having atotal duration T of 6 seconds. The tests were conducted for a period of48 hours. The positive and negative pulse magnitudes were 40 volts. Twotests, Test A and Test B, were conducted for each set of parameters. Atthe end of each test period, the height of the water in the inner tank32 was measured, and the measurement data was recorded. The results ofthe further testing is summarized in TABLE I, for the two tests, Test Aand Test B. Each pulse pattern is represented by the three numbersequence of the convention referred to above in which the first numberof the sequence is the positive pulse duration T+, the second number ofthe sequence is the negative pulse duration T-, and the third number ofthe sequence is the neutral pulse duration T_(p).

                  TABLE I                                                         ______________________________________                                                       Increase in Height                                             Pulse Pattern    Test A  Test B                                               ______________________________________                                        85-5-10          38 mm   30 mm                                                90-5-5           52 mm   38 mm                                                75-20-5          41 mm   26 mm                                                80-15-5          48 mm   33 mm                                                85-10-5          53 mm   37 mm                                                70-29-1          31 mm   22 mm                                                80-19-1          45 mm   32 mm                                                90-9-1           60 mm   43 mm                                                70-1-29          47 mm   34 mm                                                80-1-19          54 mm   38 mm                                                90-1-9           57 mm   41 mm                                                95-1-4           58 mm   45 mm                                                ______________________________________                                    

The difference in the results for Test A and Test B can be attributed todifferent chloride and pH levels in both the water and the brick 35. Toconfirm the results of these tests, further testing was conducted usingpulse patterns selected from the initial tests, including pulse patterns70-1-29, 80-1-19, 90-1-9 and 95-1-4 along with another pulse pattern85-1-14. For these tests, each of the pulse patterns had a pulse periodT of six seconds. The pulse patterns included equal positive andnegative pulse amplitudes of 40 volts D.C. The test for each pulsepattern was conducted for a period of 48 hours. The height of the waterin the inner tank was measured at the end of each of the tests. Theresults of these tests are summarized in TABLE II. The test data,arranged in ascending order for the positive pulse duration,demonstrates that a greater increase in height of the water was providedfor longer positive pulse periods. The increase in the height of thewater in the inner tank ranged from 30 mm to 45 mm for Test A and from40 mm to 55 mm for Test B. The greatest increase in height was providedfor the pulse pattern 95-1-4, which had the longest positive pulseduration for this series of tests.

                  TABLE II                                                        ______________________________________                                                       Increase in Height                                             Pulse Pattern    Test A  Test B                                               ______________________________________                                        70-1-29          30 mm   40 mm                                                80-1-19          35 mm   45 mm                                                85-1-14          37 mm   47 mm                                                90-1-9           42 mm   54 mm                                                95-1-4           45 mm   55 mm                                                ______________________________________                                    

In view of the favorable results obtained using the pulse pattern 95-1-4for the 48 hour test period, further testing was conducted over a longertime period, which was twelve days for these tests. The further testingwas conducted using the pulse pattern 95-1-4 and having a pulse period Tequal to six seconds, and with equal positive and negative pulseamplitudes of 40 volts D.C. At the end of each test period, the heightof the water in the inner tank 32 was measured and the measurement wasrecorded.

The results obtained for the further testing are summarized in TABLE IIIfor two tests with the measurement data obtained for the two tests beinglabeled Test A and Test B. As can be seen, for Test A, the height of thewater in the inner tank 32 (FIG. 5B) increased from 0 to 310 mm in thetwelve day test period. For Test B, the height in the water in the innertank increased from 0 to 245 mm in twelve days. The difference in theresults between Test A and Test B can be attributed to differentchloride and pH levels in both the water and the brick 35.

                  TABLE III                                                       ______________________________________                                                         Increase in Height                                           Date (time)            Test A  Test B                                         ______________________________________                                        3/25    (1510)          0 mm    0 mm                                          3/26    (2030)          31 mm   20 mm                                         3/27    (1905)          53 mm   37 mm                                         3/28    (0930)          70 mm   51 mm                                         3/29    (1345)          96 mm   70 mm                                         4/01    (0820)         157 mm  118 mm                                         4/02    (1420)         182 mm  138 mm                                         4/03    (1320)         200 mm  153 mm                                         4/06    (1140)         250 mm  192 mm                                         4/07    (2045)         274 mm  212 mm                                         4/09    (0955)         296 mm  231 mm                                         4/10    (0750)         310 mm  245 mm                                         ______________________________________                                    

In contrast, using the known pulse pattern 70-10-20, as disclosed inU.S. Pat. No. 5,368,709, the height of the water in the inner tankincreased from 0 to only 30 mm over a period of three days. Nomeasurable increase in height was noted after the first three days.

Further testing was conducted in which the percentage of the positivepulse time, i.e., the positive pulse duration T+, was selected to be0.90 T and 0.95 T for a pulse pattern duration T of 6 seconds. In thetwo tests, Test A and Test B, for which T+ was 0.90 T, the negativepulse duration T-was increased to 0.05 T. In the tests, Test A and TestB, for which T+ was 0.95, the negative pulse duration T- was increasedto 0.04 T. The results of these tests are summarized in TABLE IV.

                  TABLE IV                                                        ______________________________________                                                       Increase in Height                                             Pulse Pattern    Test A  Test B                                               ______________________________________                                        95-4-1           51 mm   40 mm                                                90-5-5           45 mm   36 mm                                                ______________________________________                                    

For Test B which used the pulse pattern 95-4-1, the increase in theheight of the water was 40 mm.

Further testing was conducted in which the percentage of the positivepulse time, i.e., the positive pulse duration T+, was decreased, and thenegative pulse duration T- was increased. The results of these tests aresummarized in TABLES V and VI.

                  TABLE V                                                         ______________________________________                                                       Increase in Height                                             Pulse Pattern    Test A  Test B                                               ______________________________________                                        75-10-15         39 mm   30 mm                                                80-10-10         40 mm   32 mm                                                ______________________________________                                    

                  TABLE VI                                                        ______________________________________                                                       Increase in Height                                             Pulse Pattern    Test A  Test B                                               ______________________________________                                        60-15-25         28 mm   20 mm                                                70-10-20         37 mm   28 mm                                                ______________________________________                                    

As can be seen, using a smaller percentage positive pulse durationresulted in a reduced increase in the height of the water in the innertank. In particular, the pulse pattern 70-10-20, which is similar tothat used in the U.S. Pat. No. 5,368,709, provided an increase of onlyabout 28 to 37 mm with the longer pulse pattern duration of 6 seconds,as compared to the 1.4 second pulse pattern which is disclosed in thispatent.

Although the use of smaller percentage positive pulse durations mayresult in smaller increases in the height of the water in the innertank, in preferred embodiments, pulse patterns having 0.70 T<T+≦0.97 T;0.01 T<T-≦0.05 T; 0.02 T<T_(p) ≦0.25 T can be used to provide betterresults than prior art methods and apparatus. Moreover, although themost favorable results are obtained when the duration of the pulsepattern is between about 6 and 10 seconds, pulse patterns having aduration of 3 seconds <T≦60 seconds are quite effective.

For porous materials in particular, T+=0.95 T; T-=0.01 T; and T_(p)=0.04 T, (FIG. 6A) provide a dehydrating efficiency which issignificantly better than that yielded by the prior art pulse patternshown in FIG. 5A. The long time laboratory testing with a pulse patternaccording to this embodiment of the invention has shown that the presentinvention provides a method that, even for a long term dehydrationprocess, eliminates reverse travel of the dehydrating fluid. In theabove-mentioned laboratory test, the water column level (curve II inFIG. 7) rose steadily over the test period at a rate 10 times as greatas that of the prior art pulse pattern (curve I in FIG. 7). Although thepulse pattern, according to the invention, can provide positive andnegative pulses of substantially equal magnitude, a pulse pattern wherethe positive and negative pulse amplitudes are unequal can also be usedeffectively. The positive pulse preferably is selected in the range fromabout +12 volts to +250 volts D.C. The negative pulse preferably isselected in the range from about -12 volts to about -250 volts D.C.

The total pulse period T can be greater than 3 seconds, but, less thanor equal to 60 seconds. In a most highly preferred embodiment, the pulseperiod T between about 6 and 10 seconds. However, it would be possibleto set the duration of the total pulse period T to other values in therange, while retaining the pulse duration ranges for T+, T- and T_(p) asindicated above.

According to a further aspect of the invention, an even greater osmoticpressure can be developed within the context of the invention bydividing the positive pulse duration of each pulse period T into two ormore separate positive pulses T₁ + and T₂ + separated by at least one ofeither a short duration (e.g. 0.05 T) neutral pulse T_(p1), as shown inFIG. 6B or negative pulse T₁ - as shown in FIG. 6C. In one preferredembodiment, the pulse durations of the pulse pattern of FIG. 6B, in theorder of occurrence in the period T, are as follows:

    T.sub.1 +=0.2 T; T.sub.p1 =0.05 T; T.sub.2 +=0.6; T-=0.01 T; T.sub.p2 =0.1T

where T_(p2) is the second occurrence of a neutral pulse within theperiod T.

In a highly preferred embodiment, the pulse durations of the pulsepattern of FIG. 6B, in the order of occurrence in the pulse period T areas follows:

    T.sub.1 +=0.2 T; T.sub.p1 =0.05 T; T.sub.2 +=0.7; T-=0.02 T; T.sub.p2 =0.3T

where T_(p2) is the second occurrence of a neutral pulse within theperiod T having a 10 second duration.

In yet another embodiment, the pulse pattern was:

    T.sub.1 +=0.15 T; T.sub.p1 =0.05 T; T.sub.2 +=0.60; T-=0.05 T; T.sub.p2 =0.15 T

where T_(p2) is the second occurrence of a neutral pulse within theperiod T. The duration of the period T was 10 seconds.

In one embodiment, the pulse durations of the pulse pattern of FIG. 6C,in the order of occurrence in the pulse period T are as follows:

    T.sub.1 +=0.2 T; T.sub.1 -=0.05 T; T.sub.2 +=0.6; T.sub.2 -=0.05 T; T.sub.p =0.1 T

where T₂ - is the second occurrence of a negative pulse within theperiod T.

Further testing was conducted using the highly preferred pulse patternin which T₁ +=0.2 T; T_(p1) =0.05 T; T₂ +=0.7; T-=0.02 T; T_(p2) =0.3 T,and wherein duration of the period T was 10 seconds. For the test usingthis pulse pattern, the height of the water in the inner tank increasedby 420 mm. This represented a 25% increase over the 310 height increasethat was obtained using a pulse pattern 95-1-4, for which the period Twas ten seconds. As has been stated above, the height increase providedusing the pulse pattern 95-1-4 was ten times greater than that producedusing the known pulse pattern of 70-10-20.

The results of the previously discussed laboratory test with pulsedurations as shown in FIGS. 6B and 6C show an even greater rate ofincrease in osmotic pressure, the water level reaching 40 mm of after 48hours and continuing to rise thereafter to 420 mm in a twelve day testperiod.

An important advantage of using the method and apparatus of theinvention for dehydrating porous material is that power consumption isless than that for known electro-osmotic processes. The pulse patternsand pulse pattern durations according to the invention cause a higherlevel of moisture to be removed from the porous structure in a shorterperiod of time as compared to results obtained using known techniques.As the porous material becomes dryer, electrical power use decreasesautomatically due to the lack of moisture and increased resistance ofthe porous material.

The present invention also reduces the relative humidity of the porousstructure to a stable level of about 50 percent, compared to stablelevels of about 80 percent or greater left by prior art methods andapparatus. Tests were conducted to determine the reduction in relativehumidity levels provided by different pulse patterns. The tests wereconducted in a containment structure having porous walls that arenormally subjected to very high relative humidity, at levels exceeding90 percent. In conducting these tests, a humidity sensor was insertedinto a hole approximately 1 inch deep in a wall of the containmentstructure.

One test conducted used the known pulse pattern as disclosed in U.S.Pat. No. 5,368,709, having the characteristic of FIG. 5, with a positiveduration T+ of 70 percent, a negative duration T- of 10 percent and aneutral duration T_(p) of 20 percent. The pulse pattern was applied tothe anode relative to the cathode. The duration of the pulse pattern was1.3 seconds. This pulse pattern (70-10-20) resulted in a reduction inrelative humidity of the porous material to a stable level of about 79percent.

Further testing was conducted using the pulse pattern in accordance withthe invention which had the characteristic of FIG. 6B, in which thepositive pulse duration of each pulse period T is divided into separatepositive pulses T₁ + and T₂ +, separated by a short duration pulseneutral pulse T_(p1), and followed by a negative pulse T- which, inturn, was followed by a further neutral pulse T_(p2). For one test thatwas conducted, the pulse pattern was: T₁ +=0.15 T; T_(p1) =0.05 T; T₂+=0.60; T-=0.05 T; T_(p2) =0.15 T. The duration of the period T was 10seconds. For this testing, the humidity sensor was located in the samehole in the wall of the structure that was used for the test that usedthe known pulse pattern. The pulse pattern was applied to the anoderelative to the cathode. The further testing was conducted after a delayin time, following the test using the known pulse pattern, sufficient toallow the relative humidity of the porous material to be returned tonear 90 percent. This pulse pattern (15-5-60-5-15) resulted in areduction in relative humidity of the porous material to a stable levelof about 52 percent. In general, mold growth cannot be supported below65 percent relative humidity. It is well known that harmful funguscannot survive or grow at relative humidity levels provided by thepresent invention. In addition, recent testing has confirmed thatelectro-osmotic pulsing can be used to deter radon gas penetration.Preliminary results have shown a potential 85% reduction in radondiffusion when the electro-osmotic pulsing system is in operation. Thus,the present invention can be used for reducing radon in homes and otherbuildings. Accordingly, contaminated structures can now be saved usingthe present invention.

FIG. 8 shows a circuit diagram illustrating another feature of theinvention, wherein a sensing system 40 is connected in the circuitbetween the anodes 4 and the cathode 5 sensing various parameter valuesto determine if the electro-osmotic system is functioning properly. Ifthe parameter values sensed exceed predetermined limits, the sensingsystem 40 produces an alarm signal on the line 42 which is input topower control unit 6 for producing either a visual alarm in the form ofa light 44 or an audible alarm 46.

The sensing system 40 can sense, for example, when there is a loss ofoutput power in power control unit 6. Loss of output power would beindicated if the voltage between the anodes 4 and the cathode 5 is zerofor a predetermined period of time. Additionally, the sensing system 40can determine if an upper voltage of lower voltage limit is exceeded,whether an upper current limit is exceeded or whether there is a suddencurrent drop, all of which can indicate a system error. The sensingsystem 40 can be implemented by a microcontroller which can beprogrammed for sensing the above parameters as well as other importantsystem parameters. The power control unit 6 can itself have internalsensors for activating visual alarm 44 or audible alarm 46. For example,the power control unit 6 can include a temperature sensor (not shown)for producing a signal if the temperature within the power control unit6 exceeds a predetermined limit indicating a system problem.

The electro-osmotic dehydration methods and apparatus of the inventionare not only applicable to conventional masonry and concrete, but can beapplied to any containment structure made of porous material including,for example, a clay containment structure of a landfill.

The invention has been described in detail with respect to preferredembodiments, and it will now be apparent from the foregoing to thoseskilled in the art, that changes and modifications can be made withoutdeparting from the invention in its broader aspects, and the invention,therefore, as defined in the appended claims, is intended to cover allsuch changes and modifications as to fall within the true spirit of theinvention.

What is claimed is:
 1. A method for dehydrating a porous material usingelectro-osmosis, comprising the steps of:applying a pattern of D.C.voltage pulses to an anode system embedded in the porous material, theanode system being electrically interactive with a cathode structureembedded in earth, wherein the pattern of D.C. voltage pulses has apulse period T in a range from about 3 to about 60 seconds, and eachpulse period T includes a positive pulse duration of T+ from about 0.7Tto about 0.97T, a negative pulse duration of T- from about 0.01T toabout 0.05T, and a neutral pulse duration of T_(p) from about 0.02T toabout 0.25T, and wherein each pulse period includes at least twopositive pulses separated by at least one of a second negative pulse anda second neutral pulse, and the positive pulse duration of each pulseperiod comprises a combined duration of the two positive pulses.
 2. Themethod according to claim 1, wherein each pulse period includes positiveand negative pulses of substantially equal voltage magnitudes.
 3. Themethod according to claim 1, wherein each pulse period includes positiveand negative pulses of unequal voltage magnitudes.
 4. The methodaccording to claim 1, wherein each pulse period includes positive andnegative pulses having voltage magnitudes in a range from about 12 voltsto about 250 volts.
 5. The method according to claim 1, wherein0.80T≧T+≧0.95T; 0.01T ≧T-≧0.05T and 0.04T≧T_(p) ≧0.15T.
 6. The methodaccording to claim 1, wherein 0.90T≧T+≧0.95T; 0.01T ≧T-≧0.05T and0.1T≧T_(p) ≧0.05T.
 7. The method according to claim 1, wherein the pulseperiod duration T is between about 6 seconds and 10 seconds.
 8. Themethod according to claim 1, wherein said at least two positive pulsesare separated solely by said at least one of a second negative pulse anda second neutral pulse.
 9. The method according to claim 8, wherein 0.8T≧T+≧0.95 T; 0.01 T ≧T-≧0.05T and 0.04 T≧T_(p) ≧0.15 T.
 10. The methodaccording to claim 1, wherein the two positive pulses are separated byonly a negative pulse.
 11. The method according to claim 1, wherein thetwo positive pulses are separated by only a neutral pulse.
 12. Themethod according to claim 1, wherein the two positive pulses are ofunequal duration.
 13. The method according to claim 12, wherein a ratioof the duration of the two positive pulses is at least 1:3.
 14. Themethod according to claim 1, further comprising: connecting a sensingsystem in circuit with the anode system and cathode structure forsensing system parameter values outside predetermined limits; andgenerating an alarm when the predetermined limits are exceeded.
 15. Themethod according to claim 14, wherein the system parameters that aresensed include at least one of loss of power for a given time period, anupper voltage limit, a lower voltage limit, an upper current limit and asudden current drop.
 16. A method for dehydrating a porous materialusing electro-osmosis, comprising the steps of:applying a pattern ofD.C. voltage pulses to an anode system embedded in the porous material,the anode system being electrically interactive with a cathode structureembedded in earth, wherein the pattern of D.C. voltage pulses has apulse period T, and each pulse period T includes a positive pulseduration of T+, a negative pulse duration of T-, and a neutral pulseduration of T_(p), and wherein at least the positive pulse durationincludes at least first and second pulses separated from one another byat least one of a negative pulse and a neutral pulse.
 17. An apparatusfor dehydrating a porous material using electro-osmosis, comprising:ananode system; a voltage generator for producing direct current voltagepulses to be applied to the anode system; a cathode structure embeddedin earth and located to interact electrically with at least a portion ofthe anode system; a controller for controlling the voltage generator toproduce a pattern of the direct voltage pulses having a pulse period Tin a range from about 3 to about 60 seconds, and each pulse period Tincludes a positive pulse duration of T+ from about 0.7T to about 0.97T,a negative pulse duration of T- from about 0.01T to about 0.05T, and aneutral pulse duration of T_(p) from about 0.02T to about 0.25T, andwherein each pulse period includes at least two positive pulsesseparated by at least one of a second negative pulse and a secondneutral pulse, and the positive pulse duration of each pulse periodcomprises a combined duration of the two positive pulses.
 18. Theapparatus according to claim 17, wherein the controller is programmableto provide a positive pulse duration of T+ from about 0.80T to about0.95T, a negative pulse duration of T- from about 0.01T to about 0.05Tand a neutral pulse duration T from about 0.04 to 0.15.
 19. Theapparatus according to claim 17, wherein the controller is programmableto provide a positive pulse duration of T+ from about 0.90T to about0.95T, a negative pulse duration of T- from about 0.01T to about 0.05Tand a neutral pulse period T_(p) from about 0.01T to about 0.05 T. 20.The apparatus according to claim 17, wherein the pulse period duration Tis between about 6 seconds and 10 seconds.
 21. The apparatus accordingto claim 17, wherein the two positive pulses are separated by only aneutral pulse.
 22. The apparatus according to claim 17, wherein the twopositive pulses are separated by only a negative pulse.
 23. Theapparatus according to claim 17, wherein the two positive pulses are ofunequal duration.